The invention relates to a process for the continuous removal of a gum phase from triglyceride oil resulting in gums with a low oil content and a degummed oil with a low content of gums. More particularly the invention relates to a degumming process which results in a very low refining loss of oil and in a preferred embodiment yields an oil that can be physically refined.
Crude triglyceride oils as obtained by pressing and/or extracting oil seeds or animal matter contain several compounds other than triglycerides. Some of these, such as diglycerides, tocopherols, sterols and sterol esters need not necessarily be removed during refining but other compounds such as phosphatides, free fatty acids, odors, colouring matter, waxes and metal compounds must be removed because they adversely affect taste, smell, appearance and keepability of the refined oil.
Several processes are known for the removal of these unwanted compounds and the phosphatides in particular. A commonly used process is the water degumming process during which water or steam (e.g. 3% for crude soy bean oil) is added to hot (e.g. 70.degree. C.) crude oil as a result of which most of the phosphatides present in the crude oil are hydrated and form a separate phase. This phase can then be removed for which removal process disc centrifuges are commonly used. The sludge thus removed from the oil contains water, hydratable phosphatides, triglyceride oil and several other compounds such as meal particles and glycolipids of an as yet ill-defined nature. This sludge is commonly dried to yield commercial lecithin. Water degummed oil has the advantage over crude oil that it does not throw a deposit during transport and storage.
Water degummed oil, however, still contains phosphatides, the so-called non-hydratable phosphatides (NHP) which must be removed during subsequent refining operations. British Patent 1 565 569 overcomes this problem of two stage phosphatide removal by adding an acid to the crude oil, allowing a contact time of approximately 10 min and then partially neutralizing this acid by a base, allowing an extended contact time for the development of a separate gum phase which is then separated from the oil either by gravity or centrifuge. Because of the transport and storage difficulties of crude oil, this process can only be carried out at a crushing plant which situation, on the other hand, has the advantage of providing a means of disposal of the gums thus obtained: They are passed to the meal desolventizer or are added to the meal being pelletized.
For the removal of NHP from water degummed vegetable oil a number of processes exist. In DE-AS 26 09 705 a process is described in which water degummed oil is treated with an acid and cooled to below 40.degree. C. whereupon the NHP's form gums in a form that can be removed e.g. by centrifuge. In the specification it is noted that less acid is required if a crude oil is used instead of a water degummed oil, which discovery has led to another process as described in East German Patent 132 877 in which process lecithin is added to water degummed oil to facilitate the NHP removal.
Another process to remove NHP from water degummed oil is described in U.S. Pat. No. 4,698,185. In a first stage of this process a nontoxic aqueous acid, e.g. phosphoric acid, is finely dispersed in the water degummed oil and sufficient contact time is allowed to complete the decomposition of the metal salts of phosphatidic acid constituting the NHP. In a second stage a base is added to raise the pH above 2.5 without substantial formation of soap and in a third stage the aqueous phase containing the gums and the oil phase are separated.
However, to be economically viable, the above processes must ensure that (I) the oil content of the gums is as low as possible, because this oil content constitutes a refining loss, and (II) the gum content of the oil is as low as possible, especially when the degummed oil is to be physically refined subsequently. Several of the processes described above therefore recommend washing the oil with water after the gum separation stage. This washing process, however, has the disadvantage that it again leads to oil losses and may cause pollution and/or effluent disposal problems and still leads to an insufficiently low residual phosphatide content.